The present invention relates to a light scanning device for use in a laser printer, a facsimile transmitter/receiver, a platemaking machine, or the like.
Light scanning devices employing a light deflector such as a rotating polygonal mirror for deflecting a light beam at a constant angular speed are used in laser printers, facsimile transmitter/receivers, platemaking machines, and the like. If the reflection surface of the light deflector had an accuracy error, the direction of travel of the deflected light beam would vary in a plane normal to a deflection plane that is formed by a line perpendicular to the reflection surface as it is angularly moved, resulting in pitch irregularities of the scanning line on a scanned surface and hence in low image quality. In view of this problem, there have been proposed various optical scanning systems for preventing pitch irregularities of the scanning line on a scanned surface even when the direction of travel of the deflected light beam varies in a plane normal to the deflection plane. Examples of such proposed optical scanning systems are disclosed in Japanese Laid-Open Patent Publications Nos. 59-147316 and 60-100118.
The arrangement shown in Japanese Laid-Open Patent Publication No. 59-147316 can provide a large deflection angle, but fails to sufficiently correct the curvature of field in both main and auxiliary scanning directions, with the result that a high-density spot diameter cannot be achieved. While field curvature in the main scanning direction can well be corrected in Japanese Laid-Open Patent Publication No. 60-100118, much consideration is not given to removal of pitch irregularities of the scanning line.